Support is requested for a Keystone Symposia meeting entitled Cancer Pathophysiology: Integrating the Host and Tumor Environments, organized by Sheila A. Stewart, Sandra S. McAllister and Lisa M. Coussens. The meeting will be held in Breckenridge, Colorado from March 28-April 2, 2016. The local and systemic tumor microenvironments (TME) play a pivotal role in all stages of cancer development, including initiation, malignant conversion and metastasis, as well as regulating how neoplastic cells respond to cytotoxic, targeted and immune-based therapies. Research over the last decade has revealed the incredible diversity and plasticity that constitute the TME. Thus, the focus of this meeting will be to bring together a wide range of experts who focus on the various aspects of the TME with the intent of creating a more complete picture of the potential therapeutic landscape. The unique feature of this meeting is its breadth of experts focused on both the systemic and local TME, who also recognize varied paracrine interactions with heterogeneous neoplastic cells. Presentations will focus on emerging studies, enabling attendee's access to senior investigators, as well as new investigators spanning the diversity of disciplines called cancer biology.